1. Field of the Invention
The present invention relates to a technology of measuring a magnetic particle quantity included in a liquid using a magnetic sensor, and more particularly, to an immunoassay measuring technology of measuring a protein, such as an antigen, an antibody, a tumor marker, a cell component or a very small quantity of hormone material, and the like.
2. Description of the Related Arts
Recently, an immunological measuring method (Patent Document 1: see Japanese Patent Application Laid-Open Publication (JP-A) No. 2001-33455) that is based on an antigen-antibody reaction as a principle is mainly used for inspection items, such as allergy, infectious disease, tumor marker, thyroid hormone, and the like. As the immunological measuring method, there are various highly sensitive measurement methods, such as a radio immunoassay (RIA) using a radioisotope, an enzyme immunoassay (EIA) using an enzyme, and a chemiluminescent enzyme immunoassay (CLEIA) combining an enzyme and chemiluminescent substrate. Meanwhile, for the highly sensitive immunological measuring method, tubidimetric immunoassays have been frequently used in view of handling easiness. The turbidimetric immunoassays are a method that uses one to several kinds of antibodies and detects an object to be measured based on an antigen-antibody reaction sandwiching an antigen with the antibodies and a change in turbidity or transmittance of a solution in supernatant as an index after precipitating composites generated by the reaction. These optical methods measure turbidity or coloring of a solution and a change in a very small quantity of fluorescent and luminescent materials to detect the object to be measured. These methods generally require a process (bound/free separation) of cleaning non-coupled markers occurring during the reaction process, which leads to complexity of a working process. Further, when there is turbidity or coloring in a reaction solution, there is a problem in that the detection precision may be degraded.
An example for addressing the problem may include the magnetic measuring technology. The magnetic measurement means a method of detecting a magnetic particle coupled with the object to be measured using a magnetic sensor. As the method, a magnetic susceptibility measurement, a residual magnetism measurement, and the like, due to the difference in a measurement principle of a magnetic particle have been reported (see Non-Patent Document 1: K. Enpuku et al. Jpn. J. Appl. Phys. 38, p. L1102 (1999), Non-Patent Document 2: Y. R. Chemla et al. Proc. Nat 1. Acad. Sci. USA 97, p. 14268 (2000), and Non-Patent Document 3: R. Koetitz et al. IEEE Trans. App 1. Supercond. 7, p. 3678 (1997)). Further, an AC magnetic susceptibility measurement method of measuring a quantity of surplus magnetic particles, which are not coupled with the object to be measured, as magnetic signals is disclosed in Non-Patent Document 4 (R. Kawabata et al. IEEE Sensors Conference (2010)). For the immunoassay such as ELISA, and the like, a process of cleaning and removing surplus markers, and the like, which are not coupled with the object to be measured, is required, but the method disclosed in Non-Patent Document 4 does not require a cleaning process and therefore can implement a fast measurement. In addition, since the method does not require cooling of a magnetic sensor or a magnetic film, a configuration of an apparatus can be simplified.